Study of HRO761 Alone or in Combination in Cancer Patients With Specific DNA Alterations Called Microsatellite Instability or Mismatch Repair Deficiency.

The main purpose of the study is to evaluate the safety and tolerability of HRO761 and identify the recommended dose(s), i.e., the optimal safe and active dose of HRO761 alone or in combination with pembrolizumab or irinotecan that can be given to patients who have cancers with specific molecular alterations called MSIhi (Microsatellite Instability-high) or dMMR (Mismatch Repair Deficient) that might work best to treat these specific cancer types and to understand how well HRO761 is able to treat those cancers.